1. Field of the Invention
This invention relates to a device and process for lighting a fluorescent discharge lamp, and more particularly it relates to a device and process for lighting a fluorescent discharge lamp which lights a fluorescent discharge lamp with a high-frequency pulse voltage generated by a circuit using substantially no stabilizing loads.
2. Prior Art
Generally, a fluorescent discharge lamp, in starting electric discharge from the cold cathode thereof, inherently requires a voltage roughly several times the terminal voltage used during the period of sustained discharge to be applied between the terminals of the cold cathode. For this purpose, the fluorescent discharge lamp is provided at the opposite terminals thereof with filaments which, on being heated, emit thermoelectrons and start electric discharge with a relatively low voltage. During the period of sustained electric discharge, if an increase occurs in the supplied current, the fluorescent discharge lamp retains the so-called negative characteristic, i.e., the nature that the voltage between the terminals shows a value approximating a fixed level. To ensure stable lighting of the fluorescent discharge lamp, therefore, the fluorescent discharge lamp requires a lighting device which is capable, at the time of starting electric discharge, of allowing a voltage exceeding the voltage used by the fluorescent discharge lamp for sustained electric discharge to be applied between the opposite electrodes of the fluorescent discharge lamp and, after the lamp has been lit up, regulating the electric current flowing to the fluorescent discharge lamp and, at the same time, stabilizing the incoming electric current of the fluorescent discharge lamp enough to withstand a possible variation in the voltage of the power source by virtue of a load (such as inductance, capacitance, or resistance) connected serially to the fluorescent discharge lamp, and enabling the fluorescent discharge lamp to be lit up in a stable state at all times.
The lighting devices for fluorescent discharge lamps currently in most popular use preponderantly utilize power sources of commercial frequency directly. With the voltage of common use (100 V or 200 V), they cannot cause their cold cathodes to start electric discharge. They, therefore rely on a glow lamp to heat the filaments of the fluorescent discharge lamp temporarily in order to effect emission of thermoelectrons, lower the voltage for starting electric discharge, and induce electric discharge. After the electric discharge is started, they rely on a load connected serially thereto to regulate the electric current used for the electric discharge.
The lighting device for the fluorescent discharge lamp of the nature described above, however, has the disadvantage that much time is spent in inducing the electric discharge and the volume, weight, and power loss of the inductance used for regulating the electric current for the electric discharge are large.
Recently, lighting devices for fluorescent discharge lamps which use semiconductors for the purpose of precluding the disadvantage of the conventional lighting devices have been finding actual adoption.
A typical example of these lighting devices of fluorescent discharge lamps is illustrated in FIG. 3 and is constructed as described below.
To an AC power source, a capacitor 102 and a capacitor 103 are parallely-connected through the medium of a fuse 101 and the AC input terminal of a full-wave rectifier 106 is also connected through the medium of an inductance 104 which is serially-connected to the fuse 101. To a plus terminal of the full-wave rectifier 106 is connected a resistor 105. Through the medium of the resistor 105, serially-connected circuits of a capacitor 107, a resistor 108, a resistor 109, and a diode 110 are connected to a minus terminal of the full-wave rectifier 106. A capacitor 111 is connected between the junction point between the resistor 108 and the resistor 109 and one terminal of the full-wave rectifier 106. The base of a transistor 114 is connected to the junction point through the medium of a parallely-connected circuit of a resistor 112 and an inductance 113.
Further, interposed between the collector terminal of the transistor 114 and resistor 105 is connected a parallel circuit comprising a capacitor 120 and an inductance 118. The emitter terminal of the transistor 114 is connected, through the medium of a diode 115, to a transformer winding 117 which is connected to one terminal of the full-wave rectifier 106. The collector and the emitter of the transistor 114 are interconnected with a diode 116. To the collector terminal of the transistor 114 is connected a transformer winding 119. Transformer winding 119 is connected through transformer winding 124 to an element of one filament 126 of a fluorescent lamp 127. The like element of the other filament 126 is connected to the resistor 105. The other elements of the two filaments 126 are connected serially in a curcuit comprising a trigger diode 121, a diode 122, a diode 123, and transformer winding 125.
The lighting device of a fluorescent discharge lamp which is constructed as described above is operated as follows:
First, when an AC voltage is applied to the full-wave rectifier 106, the full-wave rectifier 106 and the smoothing capacitor 107 cooperate to generate a sparingly-pulsating DC voltage.
Then, when this voltage is applied on the base of the oscillating transistor 114, an oscillating circuit composed of the inductance 118 and the capacitor 120 generates a high-frequency voltage of the order of 40 KHz closely approximating a sine wave, based on the circuit constant of the oscillating circuit.
This high-frequency voltage is boosted by the winding 119. Then, by feeding to the winding 125 a pulse voltage generated by the breakover voltage of the trigger diode 121 and, at the same time, boosting the pulse voltage with the winding 124 thereby generating a high-voltage pulse, the fluorescent discharge lamp 127 is lit up. To be specific, the filament 126 when heated emits thermoelectrons until pulses of high voltage are applied on the fluorescent discharge lamp 127 by the breakover voltage of the trigger diode 121. Thereafter the pulses of high voltage subsequently generated light up the fluorescent discharge lamp 127.
After the fluorescent discharge lamp 127 has been lit up, the high-frequency voltage which has been boosted by the winding 119 is applied on the fluorescent discharge lamp 127 and, at the same time, the electric current for the electric discharge is regulated by the winding 124 to maintain the electric discharge of the fluorescent discharge lamp 127.
In the conventional lighting device for the fluorescent discharge lamp constructed as described above, the voltage applied between the filaments 126 cannot be increased so much as to exceed the voltage for starting electric discharge of the fluorescent discharge lamp 127, even though the feedback current flowing to the transformer winding 117 may be increased. In other words, when an AC power source of 100 V is used as the power source for the lighting device of the fluorescent discharge lamp to cause oscillation of a sine wave, the oscillating voltage generated in an oscillating circuit composed of the capacitor 120 and the inductance 118 connected to the collector side of the transistor 114 is about 140 to 150 V at most. For the fluorescent discharge lamp 127 to be lit up under this condition, therefore, it requires use of a part which is capable of boosting this voltage.
The magnitude of the electric current flowing to the transformer winding 124 and the like are variable with the capacity and the type of the fluorescent discharge lamp 127. The capacity and the type of the fluorescent discharge lamp 127 which can be connected to the circuit are fixed by the capacities of the parts connected to the circuits serving to feed power to the fluorescent discharge lamp 127. When the fluorescent discharge lamp to be lit up happens to have a large capacity, the lighting device itself is required to have a large capacity, the lighting device itself is required to be proportionally large. The conventional lighting device for the fluorescent discharge lamp is such that it must be of a particular grade, exactly suiting the capacity and the type of the fluorescent discharge lamp 127 to which the lighting device is connected.
This invention has been produced for the purpose of overcoming the problem suffered by the conventional lighting device. It aims to provide a device and process for lighting a fluorescent discharge lamp, which has no need for any part serving to boost voltage, makes possible the desired light-up of a fluorescent discharge lamp without reference to the capacity and the type of the fluorescent discharge lamp to which the device is connected or the process used, and admits of interchangeability with all types of fluorescent discharge lamps.